U.S. patent number 6,927,745 [Application Number 10/647,764] was granted by the patent office on 2005-08-09 for frequency selective surfaces and phased array antennas using fluidic dielectrics.
This patent grant is currently assigned to Harris Corporation. Invention is credited to Stephen B. Brown, James J. Rawnick.
United States Patent |
6,927,745 |
Brown , et al. |
August 9, 2005 |
Frequency selective surfaces and phased array antennas using
fluidic dielectrics
Abstract
A phased array antenna (100) having a frequency selective
surface comprises a substrate (125) and an array of antenna
elements (140) thereon. Each antenna element comprises a medial
feed portion (42) and a pair of legs (49) extending outwardly
therefrom. Adjacent legs of adjacent antenna elements include
respective spaced apart end portions (51). The antenna further
comprises at least one fluidic dielectric residing within at least
one cavity (170) within the substrate and arranged between a plane
where the array of dipole antenna elements reside and a ground
plane (150), at least one composition processor (104) adapted for
dynamically changing a composition of said fluidic dielectric, and
a controller (102) for controlling the composition processor to
selectively vary at least one of a permittivity and a permeability
of the fluidic dielectric in at least one cavity in response to a
control signal (105).
Inventors: |
Brown; Stephen B. (Palm Bay,
FL), Rawnick; James J. (Palm Bay, FL) |
Assignee: |
Harris Corporation (Melbourne,
FL)
|
Family
ID: |
34273305 |
Appl.
No.: |
10/647,764 |
Filed: |
August 25, 2003 |
Current U.S.
Class: |
343/909 |
Current CPC
Class: |
H01Q
1/281 (20130101); H01Q 3/44 (20130101); H01Q
15/148 (20130101); H01Q 21/062 (20130101); H01Q
15/0013 (20130101) |
Current International
Class: |
H01Q
15/24 (20060101); H01Q 15/00 (20060101); H01Q
15/02 (20060101); H01Q 015/24 () |
Field of
Search: |
;343/909,912,781P,781CA,757,779,781R |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
US. Appl. No. 10/369,436, filed Feb. 18, 2003, Rawnick et al. .
U.S. Appl. No. 10/387,208, filed Mar. 11, 2003, Rawnick et al.
.
U.S. Appl. No. 10/330,755, filed Dec. 27, 2002, Rawnick et al.
.
U.S. Appl. No. 10/330,754, filed Dec. 27, 2002, Rawnick et al.
.
U.S. Appl. No. 10/300,456, filed Nov. 19, 2002, Rawnick et al.
.
U.S. Appl. No. 10/361,548, filed Feb. 10, 2003, Rawnick et al.
.
U.S. Appl. No. 10/387,209, filed Mar. 11, 2003, Rawnick et al.
.
U.S. Appl. No. 10/439,094, filed May 15, 2003, Killew et al. .
U.S. Appl. No. 10/387,194, filed Mar. 11, 2003, Rawnick et al.
.
U.S. Appl. No. 10/438,435, filed May 15, 2003, Rawnick et al. .
U.S. Appl. No. 10/414,696, filed Apr. 16, 2003, Rawnick et al.
.
U.S. Appl. No. 10/637,027, filed Aug. 7, 2003, Rawnick et al. .
U.S. Appl. No. 10/414,650, filed Apr. 16, 2003, Rawnick et al.
.
U.S. Appl. No. 10/635,629, filed Aug. 6, 2003, Rawnick et al. .
U.S. Appl. No. 10/459,067, filed Jun. 11, 2003, Rawnick et al.
.
U.S. Appl. No. 10/438,436, filed May 15, 2003, Rawnick et al. .
U.S. Appl. No. 10/626,090, filed Jul. 24, 2003, Rawnick et al.
.
U.S. Appl. No. 10/635,582, filed Aug. 6, 2003, Rawnick et al. .
U.S. Appl. No. 10/632,632, filed Aug. 1, 2003, Rawnick et al. .
U.S. Appl. No. 10/614,149, filed Jul. 7, 2003, Rawnick et al. .
U.S. Appl. No. 10/634,219, filed Aug. 5, 2003, Rawnick et al. .
U.S. Appl. No. 10/458,859, filed Jun. 11, 2003, Rawnick et al.
.
U.S. Appl. No. 10/624,378, filed Jul. 22, 2003, Rawnick et al.
.
U.S. Appl. No. 10/438,433, filed May 15, 2003, Rawnick et al. .
U.S. Appl. No. 10/460,947, filed Jun. 13, 2003, Rawnick et al.
.
U.S. Appl. No. 10/421,352, filed Apr. 23, 2003, Rawnick et al.
.
U.S. Appl. No. 10/409,261, filed Apr. 8, 2003, Pike. .
U.S. Appl. No. 10/441,743, filed May 19, 2003, Pike. .
U.S. Appl. No. 10/628,846, filed Jul. 28, 2003, Pike et al. .
U.S. Appl. No. 10/448,973, filed May 30, 2003, Killen et
al..
|
Primary Examiner: Wong; Don
Assistant Examiner: Cao; Huedung X.
Attorney, Agent or Firm: Sacco & Associates, PA
Claims
What is claimed is:
1. A method for beam forming a radio frequency signal radiated from
an antenna using a frequency selective surface, comprising the
steps of: propagating the radio frequency signal through the
frequency selective surface; dynamically changing the composition
of a fluidic dielectric within the frequency selective surface to
vary at least one among a permittivity and a permeability in order
to vary a propagation delay of said radio frequency signal through
the frequency selective surface.
2. The method according to claim 1, further comprising the step of
selectively adding and removing a fluidic dielectric from selected
ones of a plurality of cavities of the frequency selective surface
in response to a control signal.
3. The method according to claim 1, wherein the step of dynamically
changing the composition of fluidic dielectric comprises the step
of mixing fluidic dielectric to obtain a desired permeability and
permittivity.
4. The method according to claim 1, wherein the step of dynamically
changing the composition of fluidic dielectric comprises the step
adding and removing the fluidic dielectric to obtain a desired
permeability and permittivity.
5. A method or maintaining a constant impedance over a wide
frequency range in a phased array antenna having a frequency
selective surface, comprising the steps of: dynamically changing a
composition of a fluidic dielectric within the phased array antenna
to vary at least one among array parameters selected from the group
comprising coupling among elements of the frequency selective
surface, resonances of said elements, and an effective groundplane
spacing between said elements and a groundplane; and operating the
phased array antenna over the wide frequency range as the
composition of the fluidic dielectric is dynamically changed.
6. A phased array antenna, comprising: a frequency selective
surface; means for dynamically changing a composition of a fluidic
dielectric within the phased array antenna to vary at least one
among array parameters selected from the group comprising coupling
among elements of the frequency selective surface, resonances of
said elements, and an effective groundplane spacing between said
elements and a groundplane; means for operating the phased array
antenna over a wide frequency range as the composition of the
fluidic dielectric is dynamically changed while maintaining a
constant impedance over the wide frequency range.
Description
BACKGROUND OF THE INVENTION
1. Statement of the Technical Field
The inventive arrangements relate generally to the field of
communications, and more particularly to frequency selective
surfaces and phased array antennas.
2. Description of the Related Art
Existing microwave antennas include a wide variety of
configurations for various applications, such as satellite
reception, remote broadcasting, or military communication. The
desirable characteristics of low cost, light-weight, low profile
and mass producibility are provided in general by printed circuit
antennas. The simplest forms of printed circuit antennas are
microstrip antennas where flat conductive elements are spaced from
a single essentially continuous ground element by a dielectric
sheet of uniform thickness. An example of a microstrip antenna is
disclosed in U.S. Pat. No. 3,995,277 to Olyphant.
These antennas can be designed in an array and may be used for
communication systems such as identification of friend/foe (IFF)
systems, personal communication service (PCS) systems, satellite
communication systems, and aerospace systems, which require such
characteristics as low cost, light weight, low profile, and a low
sidelobe.
The bandwidth and directivity capabilities of such antennas,
however, can be limiting for certain applications. While the use of
electromagnetically coupled microstrip patch pairs can increase
bandwidth, obtaining this benefit presents significant design
challenges, particularly where maintenance of a low profile and
broad beam width is desirable or where a dynamically manipulated
beam is desirable. Also, the use of an array of microstrip patches
can improve directivity by providing a predetermined scan angle.
However, utilizing an array of microstrip patches presents a
dilemma. The scan angle can be increased if the array elements are
spaced closer together, but closer spacing can increase undesirable
coupling between antenna elements thereby degrading
performance.
Furthermore, while a microstrip patch antenna is advantageous in
applications requiring a conformal configuration, e.g. in aerospace
systems, mounting the antenna presents challenges with respect to
the manner in which it is fed such that conformality and
satisfactory radiation coverage and directivity are maintained and
losses to surrounding surfaces are reduced. More specifically,
increasing the bandwidth of a phased array antenna with a wide scan
angle is conventionally achieved by dividing the frequency range
into multiple bands.
One example of such an antenna is disclosed in U.S. Pat. No.
5,485,167 to Wong et al. This antenna includes several pairs of
dipole pair arrays each tuned to a different frequency band and
stacked relative to each other along the transmission/reception
direction. The highest frequency array is in front of the next
lowest frequency array and so forth.
This approach may result in a considerable increase in the size and
weight of the antenna while creating a Radio Frequency (RF)
interface problem. Another approach is to use gimbals to
mechanically obtain the required scan angle. Yet, here again, this
approach may increase the size and weight of the antenna and result
in a slower response time. The present invention utilizes a
reconfigured frequency selective surface to avoid many of these
detriments.
A frequency selective surface is typically an array of periodic
elements used to tightly couple resonant elements such as dipoles,
slots and spatial filters that reflect. A frequency selective
surface is also considered a construction that either passes or
reflects certain frequencies.
Thus, there is a need for a frequency selective surface as well as
a lightweight phased array antenna with a wide frequency bandwidth
and a wide scan angle utilizing such frequency selective surface,
and that can be conformably mountable to a surface if required.
Such a need has been met through the use of current sheet arrays or
dipole layers using interdigital capacitors that increase coupling
by lengthening the capacitor "digits" or "fingers" that result in
additional bandwidth as discussed in U.S. Pat. No. 6,417,813 to
Durham ('813 Patent) and assigned to the assignee herein. Some
antennas of this structure exhibit a significant gain dropout at
particular frequencies in the desired operational bandwidth,
spurious resonances, and possibly other undesirable
characteristics. Being able to change the phase response or the
resonant frequency across the frequency selective surface can
likely remove most of these undesirable characteristics. Thus, a
need exists for a lightweight phased array antenna with a wide
frequency bandwidth and wide scan angle that overcomes the gain
dropout and other undesirable characteristics discussed above.
The key to broad-band performance with a phased array antenna
incorporating a frequency selective surface is to achieve constant
impedance over a wide frequency range. None of the constituent
components of such an array (e.g. the elements, the unit cell
spacing, the mutual coupling, the dielectric properties of the
material layers in which the array is embedded, and the spacing
between the array and the ground plane, if any) have this constant
impedance property. However, the impedance properties of the
components all vary differently with frequency. With appropriate
choices in accordance with the invention, these individual
variations can be made to balance over a broad frequency range, so
that collectively, but not individually, the design elements of the
array achieve broadband performance. Note that this design approach
utilizes the coupling between the elements, whereas in other array
designs the coupling is considered undesirable.
In practice, the present state of the art in such arrays is limited
to about 10:1 bandwidth. This is much broader bandwidth than has
been achieved with other arrays, but there are applications which
could benefit from even more bandwidth. The limitations in practice
arise from a number of factors, including undesired resonances in
the array design, e.g. in the coupling structure, and the desired
scanning performance of the array. Embodiments in accordance with
the present invention utilize fluids to extend the range over which
the array operates, allowing the instantaneous bandwidth of the
array to be utilized over an even wider operating range. Examples
of the array parameters which could be affected by fluids are the
coupling structures, the element resonances, and the effective
ground plane spacing.
SUMMARY OF THE INVENTION
In a first aspect of the present invention, a phased array antenna
having a frequency selective surface comprises a substrate and an
array of antenna elements thereon. Each antenna element comprises a
medial feed portion and a pair of legs extending outwardly
therefrom. Adjacent legs of adjacent antenna elements include
respective spaced apart end portions. The antenna further comprises
at least one fluidic dielectric residing within at least one cavity
within the substrate and arranged between a plane where the array
of dipole antenna elements reside and a ground plane, at least one
composition processor adapted for dynamically changing a
composition of said fluidic dielectric to vary at least one of said
permittivity and said permeability in said at least one cavity, and
a controller for controlling the composition processor to
selectively vary at least one of a permittivity and a permeability
of the fluidic dielectric in at least one cavity in response to a
control signal.
In a second aspect of the present invention, a phased array antenna
comprises a substrate and an array of antenna elements thereon, at
least one fluidic dielectric having a permittivity and a
permeability able to reside within at least one cavity within at
least one dielectric layer, wherein the dielectric layer resides
between the substrate and a ground plane. The antenna further
comprises at least one composition processor adapted for
dynamically changing a composition of the fluidic dielectric in the
at least one cavity and a controller for controlling the
composition processor to selectively vary at least one of the
permittivity and the permeability in at least one cavity in
response to a control signal.
In a third aspect of the present invention, a phased array antenna
comprises a current sheet array on a substrate, at least one
dielectric layer between the current sheet array and a ground
plane, and at least one cavity within the at least one dielectric
layer for retaining at least one fluidic dielectric. The antenna
can further include at least one fluidic pump unit for adding and
removing the fluid dielectric to or from the at least one cavity in
response to a control signal.
In yet another aspect of the present invention, a method for beam
forming a radio frequency signal radiated from an antenna using a
frequency selective surface comprises the steps of propagating the
radio frequency signal through the frequency selective surface and
dynamically changing the composition of a fluidic dielectric within
the frequency selective surface to vary at least one among a
permittivity and a permeability in order to vary a propagation
delay of said radio frequency signal through the frequency
selective surface.
The spaced apart end portions of the dipole antenna elements can
preferably have a predetermined shape and be relatively positioned
to provide increased capacitive coupling between the adjacent
dipole antenna elements. The spaced apart end portions in adjacent
legs can comprise interdigitated portions, and each leg can have an
elongated body portion, an enlarged width end portion connected to
an end of the elongated body portion, and a plurality of fingers,
e.g. four, extending outwardly from the enlarged width end
portion.
The wideband phased array antenna has a desired frequency range and
the spacing between the end portions of adjacent legs is less than
about one-half a wavelength of a highest desired frequency. Also,
the array of (dipole) antenna elements may include first and second
sets of orthogonal dipole antenna elements to provide dual
polarization. A ground plane is preferably provided adjacent the
array of dipole antenna elements and is spaced from the array of
dipole antenna elements less than about one-half a wavelength of a
highest desired frequency.
Preferably, each dipole antenna element comprises a printed
conductive layer, and the array of dipole antenna elements can be
arranged at a density in a range of about 100 to 900 per square
foot. The array of dipole antenna elements is sized and relatively
positioned so that the wideband phased array antenna is operable
over a frequency range of about 2 to 30 GHz, and at a scan angle of
about .+-.60 degrees. There may be at least one dielectric-layer on
the array of dipole antenna elements, and the flexible substrate
may be supported on a rigid mounting member having a non-planar
three-dimensional shape.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram illustrating the wideband phased
array antenna in accordance with the present invention mounted on
the nosecone of an aircraft, for example.
FIG. 2 is a schematic diagram of the printed conductive layer of
the wideband phased array antenna of FIG. 1.
FIG. 3 is a schematic diagram of the printed conductive layer of
the wideband phased array antenna of another embodiment of the
wideband phased array antenna of FIG. 2.
FIGS. 4 and 5 are enlarged schematic views of the spaced apart end
portions of adjacent legs of adjacent dipole antenna elements of
the alternative embodiments of the wideband phased array antenna of
FIG. 2.
FIG. 6A is an exploded view of a wideband phased array antenna
having a frequency selective surface with cavities for fluidic
dielectrics in accordance with the present invention.
FIG. 6B is a side view of the wideband phased array antenna of FIG.
6A.
FIG. 7A is an exploded view of a wideband phased array antenna
having a frequency selective surface and a dielectric layer with
cavities for fluidic dielectrics and a conductive plane in
accordance with the present invention.
FIG. 7B is a side view of the wideband phased array antenna of FIG.
7A.
FIG. 7C is an exploded view of an alternative embodiment of the
wideband phased array antenna of FIGS. 7A & 7B further
including a conductive plane in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described more fully hereinafter
with reference to the accompanying drawings, in which preferred
embodiments of the invention are shown. This invention may,
however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout, and prime and double prime notation are used
to indicate similar elements in alternative embodiments.
Referring initially to FIGS. 1 and 2(A-C), a wideband phased array
antenna 10 in accordance with the present invention is illustrated.
The antenna 10 may be mounted on the nosecone 12, or other rigid
mounting member having either planar or a non-planar
three-dimensional shape, of an aircraft or spacecraft, for example,
and may also be connected to a transmission and reception
controller 14 as would be appreciated by the skilled artisan.
The wideband phased array antenna 10 is preferably formed of a
plurality of flexible layers as shown in FIGS. 6 and 7. These
layers can include a dipole layer or current sheet array, which is
sandwiched between a ground plane and an outer dielectric layer
such as the outer dielectric layer of foam. Other dielectric layers
and at least one coupling plane could be included. It should be
noted that the coupling plane can be embodied in many different
forms including planes that are only partially metalized or fully
metalized, coupling planes that reside above or below the dipole
layer, or multiple coupling planes that can reside either above or
below the dipole layer or both. The dielectric layers may have
tapered dielectric constants to improve the scan angle.
The current sheet array, frequency selective surface or dipole
layer typically consists of closely-coupled dipole elements
embedded in dielectric layers above a ground plane. Inter-element
coupling can be achieved with interdigital capacitors. Coupling can
be increased by lengthening the capacitor digits as shown in FIGS.
2-4. The additional coupling provides more bandwidth.
Unfortunately, sufficiently long digits will exhibit a gain
dropout, such as a 8 dB gain dropout at 15 GHz. It is believed that
the capacitors tend to act as a bank of quarter-wave (.lambda./4)
couplers. An E-field plot (not shown) confirms that cross-polarized
capacitors are resonating at a dropout frequency even though only
vertically-polarized elements are excited. Despite this, coupling
must be maintained to extend the bandwidth of a particular design.
The present invention maintains the necessary degree of
inter-element coupling by placing coupling plates on separate
layers around or adjacent to the interdigital capacitors.
Shortening the capacitor digits moves the gain dropout out of band,
but reduces coupling and bandwidth. Adding fluidic dielectrics and
optionally adding the coupling plates increases the capacitive
coupling to maintain or improve bandwidth. The use of fluidic
dielectrics and the optional coupling plates can improve bandwidth
in simple designs, where no interdigital capacitors are used as
shown in FIGS. 5-7.
Composition of the Fluidic Dielectric
The fluidic dielectric can be comprised of any fluid composition
having the required characteristics of permittivity and
permeability as may be necessary for achieving a selected range of
delay. Those skilled in the art will recognize that one or more
component parts can be mixed together to produce a desired
permeability and permittivity required for a particular time delay
or radiated energy shape. In this regard, it will be readily
appreciated that fluid miscibility can be a key consideration to
ensure proper mixing of the component parts of the fluidic
dielectric.
The fluidic dielectric also preferably has a relatively low loss
tangent to minimize the amount of RF energy lost in the antenna.
Aside from the foregoing constraints, there are relatively few
limits on the range of materials that can be used to form the
fluidic dielectric. Accordingly, those skilled in the art will
recognize that the examples of suitable fluidic dielectrics as
shall be disclosed herein are merely by way of example and are not
intended to limit in any way the scope of the invention. Also,
while component materials can be mixed in order to produce the
fluidic dielectric as described herein, it should be noted that the
invention is not so limited. Instead, the composition of the
fluidic dielectric could be formed in other ways. All such
techniques will be understood to be included within the scope of
the invention.
Those skilled in the art will recognize that a nominal value of
permittivity (.epsilon..sub.r) for fluids is approximately 2.0.
However, the fluidic dielectric used herein can include fluids with
higher values of permittivity. For example, the fluidic dielectric
material could be selected to have a permittivity values of between
2.0 and about 58, depending upon the amount of delay or energy
shape required.
Similarly, the fluidic dielectric can have a wide range of
permeability values. High levels of magnetic permeability are
commonly observed in magnetic metals such as Fe and Co. For
example, solid alloys of these materials can exhibit levels of
.mu..sub.r in excess of one thousand. By comparison, the
permeability of fluids is nominally about 1.0 and they generally do
not exhibit high levels of permeability. However, high permeability
can be achieved in a fluid by introducing metal particles/elements
to the fluid. For example typical magnetic fluids comprise
suspensions of ferro-magnetic particles in a conventional
industrial solvent such as water, toluene, mineral oil, silicone,
and so on. Other types of magnetic particles include metallic
salts, organo-metallic compounds, and other derivatives, although
Fe and Co particles are most common. The size of the magnetic
particles found in such systems is known to vary to some extent.
However, particles sizes in the range of 1 nm to 20 .mu.m are
common. The composition of particles can be selected as necessary
to achieve the required permeability in the final fluidic
dielectric. Magnetic fluid compositions are typically between about
50% to 90% particles by weight. Increasing the number of particles
will generally increase the permeability.
Example of materials that could be used to produce fluidic
dielectric materials as described herein would include oil (low
permittivity, low permeability), a solvent (high permittivity, low
permeability) and a magnetic fluid, such as combination of a
solvent and a ferrite (high permittivity and high permeability). A
hydrocarbon dielectric oil such as Vacuum Pump Oil MSDS-12602 could
be used to realize a low permittivity, low permeability fluid, low
electrical loss fluid. A low permittivity, high permeability fluid
may be realized by mixing some hydrocarbon fluid with magnetic
particles such as magnetite manufactured by FerroTec Corporation of
Nashua, N.H., or iron-nickel metal powders manufactured by Lord
Corporation of Cary, N.C. for use in ferrofluids and
magnetoresrictive (MR) fluids. Additional ingredients such as
surfactants may be included to promote uniform dispersion of the
particle. Fluids containing electrically conductive magnetic
particles require a mix ratio low enough to ensure that no
electrical path can be created in the mixture. Solvents such as
formamide inherently posses a relatively high permittivity. Similar
techniques could be used to produce fluidic dielectrics with higher
permittivity. For example, fluid permittivity could be increased by
adding high permittivity powders such as barium titanate
manufactured by Ferro Corporation of Cleveland, Ohio.
Referring now to FIGS. 2 and 4, a first embodiment of the dipole
layer 21 will now be described. The dipole layer 21 is a printed
conductive layer having an array of dipole antenna elements 40 on a
flexible substrate 23. Each dipole antenna element 40 can comprise
a medial feed portion 42 and a pair of legs 44 extending outwardly
therefrom. Respective feed lines are connected to each feed portion
42 from the opposite side of the substrate 23, as will be described
in greater detail below. Adjacent legs 44 of adjacent dipole
antenna elements 40 have respective spaced apart end portions 46 to
provide increased capacitive coupling between the adjacent dipole
antenna elements. The adjacent dipole antenna elements 40 have
predetermined shapes and relative positioning to provide the
increased capacitive coupling. For example, the capacitance between
adjacent dipole antenna elements 40 may be between about 0.016 and
0.636 picofarads (pF), and preferably between 0.159 and 0.239
pF.
Preferably, as shown in FIG. 4, the spaced apart end portions 46 in
adjacent legs 44 have overlapping or interdigitated portions 47,
and each leg 44 comprises an elongated body portion 49, an enlarged
width end portion 51 connected to an end of the elongated body
portion, and a plurality of fingers 53, for example four fingers
extending outwardly from the enlarged width end portion. The
antenna elements 40 can further comprise a cavity 70 that runs
adjacent to the antenna elements 40. In this instance, it is shown
as residing below the gap between the plurality of fingers 53,
although the phase array antenna could certainly include many other
cavities and in other configurations.
Alternatively, as shown in FIG. 5, adjacent legs 44' of adjacent
dipole antenna elements 40 may have respective spaced apart end
portions 46' to provide increased capacitive coupling between the
adjacent dipole antenna elements. In this embodiment, the spaced
apart end portions 46' in adjacent legs 44' comprise enlarged width
end portions 51' connected to an end of the elongated body portion
49' to provide the increased capacitive coupling between the
adjacent dipole antenna elements. Here, for example, the distance K
between the spaced apart end portions 46' can be about 0.003
inches.
As shown in FIG. 7C, coupling plane 217 can reside adjacent to the
dipole antenna elements preferably above or below a dipole layer
240. The coupling plane 217 can have metallization on the entire
surface of the coupling plane or metallization on select portions
of the coupling plane. Of course, other arrangements which increase
the capacitive coupling between the adjacent dipole antenna
elements are also contemplated by the present invention.
Preferably, the array of dipole antenna elements 40 are arranged at
a density in a range of about 100 to 900 per square foot. The array
of dipole antenna elements 40 are sized and relatively positioned
so that the wideband phased array antenna 10 is operable over a
frequency range of about 2 to 30 GHz, and at a scan angle of about
.+-.60 degrees (low scan loss). Such an antenna 10 may also have a
10:1 or greater bandwidth, includes conformal surface mounting,
while being relatively lightweight, and easy to manufacture at a
low cost.
For example, FIG. 4 is a greatly enlarged view showing adjacent
legs 44 of adjacent dipole antenna elements 40 having respective
spaced apart end portions 46 to provide the increased capacitive
coupling between the adjacent dipole antenna elements. In the
example, the adjacent legs 44 and respective spaced apart end
portions 46 may have the following dimensions: the length E of the
enlarged width end portion 51 equals 0.061 inches; the width F of
the elongated body portions 49 equals 0.034 inches; the combined
width G of adjacent enlarged width end portions 51 equals 0.044
inches; the combined length H of the adjacent legs 44 equals 0.276
inches; the width I of each of the plurality of fingers 53 equals
0.005 inches; and the spacing J between adjacent fingers 53 equals
0.003 inches. In the example (referring to FIG. 2), the dipole
layer 20 may have the following dimensions: a width A of twelve
inches and a height B of eighteen inches. In this example, the
number C of dipole antenna elements 40 along the width A equals 43,
and the number D of dipole antenna elements along the length B
equals 65, resulting in an array of 2795 dipole antenna
elements.
The wideband phased array antenna 10 has a desired frequency range,
e.g. 2 GHz to 18 GHz, and the spacing between the end portions 46
of adjacent legs 44 is less than about one-half a wavelength of a
highest desired frequency.
Referring to FIG. 3, another embodiment of the dipole layer 21' may
include first and second sets of dipole antenna elements 40 which
are orthogonal to each other to provide dual polarization, as would
be appreciated by the skilled artisan.
The phased array antenna 10 may be made by forming the array of
dipole antenna elements 40 on the flexible substrate 23. This
preferably includes printing and/or etching a conductive layer of
dipole antenna elements 40 on the substrate 23. As shown in FIG. 3,
first and second sets of dipole antenna elements 40 may be formed
orthogonal to each other to provide dual polarization.
Again, each dipole antenna element 40 includes the medial feed
portion 42 and the pair of legs 44 extending outwardly therefrom.
Forming the array of dipole antenna elements 40 includes shaping
and positioning respective spaced apart end portions 46 of adjacent
legs 44 of adjacent dipole antenna elements to provide increased
capacitive coupling between the adjacent dipole antenna elements.
Shaping and positioning the respective spaced apart end portions 46
preferably includes forming interdigitated portions 47 (FIG. 4) or
enlarged width end portions 51' (FIG. 5). A ground plane (see FIGS.
6-7) is preferably formed adjacent the array of dipole antenna
elements 40, and one or more dielectric layers can be layered on
either side of the dipole layer with adhesive layers therebetween
as is known in the art.
Again referring to FIG. 5, each dipole antenna element 40 includes
the medial feed portion 42 and the pair of legs 44' extending
outwardly therefrom. Forming the array of dipole antenna elements
40 includes shaping and positioning respective spaced apart end
portions 46' of adjacent legs 44' of adjacent dipole antenna
elements to provide increased capacitive coupling between the
adjacent dipole antenna elements. Shaping and positioning the
respective spaced apart end portions 46 preferably includes
enlarged width end portions 51'. The antenna elements 40 can
further comprise at least one cavity 70' that runs adjacent to the
antenna elements 40. In this instance, cavities are shown as
residing below the gap between the end portions 46' and in other
strategically placed locations, although the phase array antenna
could certainly include many other cavities and in other
configurations in accordance with the present invention.
As discussed above, the array of dipole antenna elements 40 are
preferably sized and relatively positioned so that the wideband
phased array antenna 10 is operable over a frequency range of about
2 to 30 GHz, and operable over a scan angle of about .+-.60
degrees. The antenna 10 may also be mounted on a rigid mounting
member 12 having a non-planar three-dimensional shape, such as an
aircraft, for example.
Thus, a phased array antenna 10 with a wide frequency bandwith and
a wide scan angle is obtained by utilizing tightly packed dipole
antenna elements 40 with cavities having fluidic dielectrics and
optionally with additional large mutual capacitive coupling.
Conventional approaches have sought to reduce mutual coupling
between dipoles, but the present invention makes use of, and
increases, mutual coupling between the closely spaced dipole
antenna elements to prevent grating lobes and achieve the wide
bandwidth. The antenna 10 is scannable with a beam former, and each
antenna dipole element 40 has a wide beam width. The layout of the
elements 40 could be adjusted on the flexible substrate 23 or
printed circuit board, or the bean former may be used to adjust the
path lengths of the elements to put them in phase.
The present invention can be utilized in a feedthrough lens as
described in U.S. Pat. No. 6,417,813 to Timothy Durham, assigned to
the assignee herein and hereby incorporated by reference ('813
Patent). As described in the '813 Patent, the feedthrough lens
antenna may include first and second phased array antennas (10)
that are connected by a coupling structure in back-to-back
relation. Again, each of the first and second phased array antennas
are substantially similar to the antenna 10 described above. The
coupling structure may include a plurality of transmission elements
each connecting a corresponding dipole antenna element of the first
phased array antenna with a dipole antenna element of the second
phased array antenna. The transmission elements may be coaxial
cables, for example, as illustratively shown in FIG. 6 of the '813
Patent.
By using the wide bandwidth phased array antenna 10 described
above, the feedthrough lens antenna of the present invention will
advantageously have a transmission passband with a bandwidth on the
same order. Similarly, the feedthrough lens antenna will also have
a substantially unlimited reflection band, since the phased array
antenna 10 is substantially reflective at frequencies below its
operating band. Scan compensation may also be achieved.
Additionally, the various layers of the first and second phased
array antennas may be flexible as described above, or they may be
more rigid for use in applications where strength or stability may
be necessary, as will be appreciated by those of skill in the
art.
Whether the wideband phased array antenna 10 is used by itself or
incorporated in a feedthrough lens antenna, the present invention
can preferably be used with applications requiring a continuous
bandwidth of 9:1 or greater and certainly extends the operational
bandwidth of current sheet arrays or dipole layers as described
herein.
Referring to FIGS. 6A and 6B, a schematic diagram and a side view
respectively of an antenna system 100 having at least one cavity
(and in this embodiment a plurality of cavities 170) that can
contain at least one fluidic dielectric having a permittivity and a
permeability is shown. The cavities 170 can be a plurality of tubes
such as quartz capillary tubes formed within a frequency selective
surface (or current sheet array or dipole layer) comprised of a
substrate 125 having an array of antenna elements 140 such as
dipole antenna elements formed on the substrate 125. The antenna
100 also preferably includes a conductive ground layer 150 beneath
the frequency selective surface and more particularly underneath
substrate 125. Note that antenna 100 is described as an exemplary
embodiment and that the invention is not limited to such
arrangement in terms of cavities, antenna elements, or
construction.
The antenna 100 can further include at least one composition
processor or pump 104 adapted for dynamically changing a
composition of the fluidic dielectric to vary at least the
permittivity and/or permeability in any of the plurality of
cavities 170. It should be understood that the at least one
composition processor can be independently operable for adding and
removing the fluidic dielectric from each of said plurality of
cavities. The fluidic dielectric can be moved in and out of the
respective cavities using feed lines 107 for example. The antenna
100 can further include a controller or processor 102 for
controlling the composition processor 104 to selectively vary at
least one of the permittivity and/or the permeability in at least
one of the plurality of cavities in response to a control signal.
As previously described, the fluidic dielectric used in the
cavities can be comprised of an industrial solvent having a
suspension of magnetic particles. The magnetic particles are
preferably formed of a material selected from the group consisting
of ferrite, metallic salts, and organo-metallic particles although
the invention is not limited to such compositions.
Referring again to FIG. 6A, the controller or processor 102 is
preferably provided for controlling operation of the antenna 100 in
response to a control signal 105. The controller 102 can be in the
form of a microprocessor with associated memory, a general purpose
computer, or could be implemented as a simple look-up table.
For the purpose of introducing time delay or energy shaping in
accordance with the present invention, the exact size, location and
geometry of the cavity structure as well as the permittivity and
permeability characteristics of the fluidic dielectric can play an
important role. The processor and pump or flow control device (102
and 104) can be any suitable arrangement of valves and/or pumps
and/or reservoirs as may be necessary to independently adjust the
relative amount of fluidic dielectric contained in the cavities
170. Even a MEMS type pump device (not shown) can be interposed
between the cavity or cavities and a reservoir for this purpose.
However, those skilled in the art will readily appreciate that the
invention is not so limited as MEMS type valves and/or larger scale
pump and valve devices can also be used as would be recognized by
those skilled in the art.
The flow control device can ideally cause the fluidic dielectric to
completely or partially fill any or all of the cavities 170. The
flow control device can also cause the fluidic dielectric to be
evacuated from the cavity into a reservoir. According to a
preferred embodiment, each flow control device is preferably
independently operable by controller 102 so that fluidic dielectric
can be added or removed from selected ones of the cavities 170 to
produce the required amount of delay indicated by a control signal
105.
Referring to FIGS. 7A and 7B, a schematic diagram and a side view
respectively of an alternative antenna system 200 similar to
antenna system 100 is shown. Antenna system 200 preferably includes
at least one cavity 270 that can contain at least one fluidic
dielectric. The antenna system generally comprises a frequency
selective surface including antenna members 240 on a substrate 225.
Additionally, antenna system 200 further includes a conductive
ground plane 250 below the substrate 225. In this embodiment, the
cavity or cavities 270 are formed within a separate substrate 235
(apart from the frequency selective surface) as opposed to the
cavities 170 formed in the substrate 125 of the frequency selective
surface of antenna system 100 of FIGS. 6A and 6B. As clearly shown
in FIG. 7B, the substrate 235 is placed between substrate 225 and
ground plane 250.
In one further variation of the present invention as illustrated in
FIG. 7C, the antenna system 200 can further comprise a conductive
plane 217 in addition to the elements previously described with
respect to FIG. 7B. As previously described, the conductive plane
217 provides additional coupling among the antenna elements 240.
The conductive plane 217 can be positioned between substrate 225
and substrate 235 as shown, although the present invention is not
limited to such arrangement. In any event, each of the embodiment
described in accordance with the present invention should be able
to change the phase response or the resonant frequency across the
frequency selective surface in order to remove undesirable
characteristics.
While the preferred embodiments of the invention have been
illustrated and described, it will be clear that the invention is
not so limited. Numerous modifications, changes, variations,
substitutions and equivalents will occur to those skilled in the
art without departing from the spirit and scope of the present
invention as described in the claims.
* * * * *